#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#define INF 2000000000
#define MaxN 1005
using namespace std;
    
FILE *IN,*OUT;
int N,K,v[MaxN][MaxN],Row[MaxN][MaxN],Column[MaxN][MaxN],Diag[MaxN][MaxN],D[MaxN][MaxN],S=0,Min=INF;

int main()
{
	IN=fopen("ferma2.in","r");
	OUT=fopen("ferma2.out","w");
	
	fscanf(IN,"%d%d",&N,&K);
	for(int i=1;i<=N;i++)
		for(int j=1;j<=i;j++)
		{
			fscanf(IN,"%d",&v[i][j]);
			Row[i][j]=Row[i][j-1]+v[i][j];
			Column[i][j]=Column[i-1][j]+v[i][j];
			Diag[i][j]=Diag[i-1][j-1]+v[i][j];
			S+=v[i][j];
		}
	for(int i=1;i<=N-K;i++)
		for(int j=1;j<=i;j++)
			D[0][0]+=v[i][j];
	Min=min(Min,D[0][0]);
	for(int i=1;i<=K;i++)
		D[i][0]=D[i-1][0]+Row[i+N-K][N-K]-Diag[i+N-K-1][N-K],Min=min(Min,D[i][0]);
	
	for(int i=1;i<=K;i++)
		for(int j=1;j<=i;j++)
			D[i][j]=D[i][j-1]+Column[i][j]-Column[i+N-K][j]-Diag[i][j]+Diag[i+N-K][j+N-K],Min=min(Min,D[i][j]);
	fprintf(OUT,"%d",S-Min);
	return 0;
}